Friction welding flash trap seal

ABSTRACT

A friction welded part having a sealed flash trap is disclosed, along with a method for producing such parts. The friction welded parts have a hollow cylindrical part and a second part to which the hollow cylindrical part is friction welded. There is an internal flash trap in the region of the weld, and the hollow cylindrical part is pinched inwardly or a conical flange on the flash trap is deformed outwardly so as to seal the flash collecting portions of the flash trap from the hollow portion of the hollow cylindrical part remote from the weld. The method involves the conventional steps of rotating the parts with respect to each other under pressure, stopping the rotation, and exerting high pressure to form the weld. In accordance with the invention, the hollow cylindrical part in the region adjacent the flash trap is then forced inwardly or a flange on the flash trap is forced outwardly so as to effect the seal. Rolling is the preferred method of forcing the hollow cylindrical part inwardly, and is preferably carried out immediately after the welding, so that the remaining weld heat can be used to advantage. A mandrel or punch is used if a flange on the flash trap is forced outwardly.

REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 07/052,084, filedMay 19, 1987, now U.S. Pat. No. 4,832,769.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to friction welding, and particularlyto friction welded parts having a flash trap. The invention providesfriction welded parts with a novel sealed flash trap and a method ofproducing such parts.

Friction welding is a well-known manufacturing process which uses axialforce and rotational motion to heat a circular interface (solid ortubular) by friction, plasticizing and upsetting material into "flashrolls" while losing axial length, and then arresting the rotationalmotion and usually increasing axial force, to form a solid state forgebond between two or more components. It may be performed either oncontinuous drive friction welding machines using a constant speed motordrive, or on inertia friction welding machines which store kineticenergy in a flywheel attached to the machine spindle and disperse thatenergy to the weld interface when axial force is applied, or on hybridmachines combining both methods.

Although conventional friction welding results in a totally randomstopped position, specifically equipped machines with an "angularorientation" capability may be used to align asymmetrical features onopposite sides of the symmetrical interface by stopping the machinespindle in the same location every cycle.

Flash is of course inherent in friction welding. In some applications,the flash can be ignored, but in other applications cannnot betolerated. The flash may have small particulate matter which could breakaway and cause problems, or an oxidized flash scale which may also breakfree to cause problems. In some applications, even minute particlesbreaking away from the flash cannot be tolerated. For example, inhydraulic cylinders, where the end of the cylinder may be frictionwelded to the body, contamination as small as 10 microns cannot bepermitted.

2. Description of the Prior Art

In the past, this problem has meant that friction welding could not beused for certain applications, unless elaborate steps were taken toeliminate the flash, e.g. by machining, or by using some form of sealantto seal off the area of the weld from the area to be keptuncontaminated.

External and internal (for tubular welds) flash may be removed byshearing tools, turning tools, or boring tools on the welder.Alternatively, "flash traps" may be used to partially isolate internalor external flash rolls. A flash trap, in the case of an internal flashtrap, is typically in the form of a solid cylinder of diameter slightlyless than the inner diameter of the hollow cylindrical part, extendingalong the hollow cylindrical part back from the region of the weld, andhaving an annular recess in the region of the weld. The flash is"trapped" in this annular recess. However, there must normally be someclearance between the rotating components, i.e. between the hollowcylinder and the solid flash trap cylinder, so that the concentricitylimitation (accuracy under load) of the machine used does not result in"rubbing" or "pickup" away from the friction surfaces, with consequentdamage and creation of scale and loose particulate matter. The existenceof this clearance provides a path for small particulate matter to escapethe trap. In the prior art, that clearance in flash traps of this andother configurations has been sealed by subsequent operations usingepoxy, "O" rings, conventional welding, etc., which renders theproduction of the parts somewhat uneconomical.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a tightly closed interiorflash trap, to provide an economical solution to the problem.

Thus in accordance with the present invention the hollow cylindricalpart adjacent the non-recessed portion of the flash trap is pinchedinwardly, thereby sealing the recessed area of the flash trap from thehollow portion of the hollow cylindrical part remote from the weld.

Alternatively, the flash trap includes an annular conical flange whichis deformed outwardly, thereby sealing the recessed area of the flashtrap from the hollow portion of the hollow cylindrical part remote fromthe weld.

In accordance with the method, as described and claimed in the relatedapplication, the conventional steps of rotating the parts with respectto each other under pressure, stopping the rotation, and exerting highpressure to form the weld, are improved by then forcing the hollowcylindrical part adjacent the non-recessed portion of the flash trapinwardly against the non-recessed portion of the flash trap, or byforcing an annular conical flange on the flash trap outwardly, therebysealing the recessed area of the flash trap from the hollow portion ofhollow cylindrical part remote from the weld. This step is preferablycarried out immediately after the welding, so that the remaining weldheat can be used.

Further features of the invention will be described or will becomeapparent in the course of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more clearly understood, thepreferred embodiment thereof and the preferred method will now bedescribed in detail by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 is a sectional illustration of a part produced in accordance withthe prior art;

FIG. 2 is a sectional illustration of a corresponding part as producedaccording to the invention;

FIG. 3 is a sectional illustration showing an alternative flash traparrangement;

FIG. 4 is a sectional illustration showing yet another alternative flashtrap arrangement; and

FIG. 5 is a sectional illustration showing a part in which the flashtrap has an annular conical flange which is deformed instead of thehollow cylinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a sectional view of a typical part produced according tothe prior art, and FIG. 2 shows a sectional view of a typical partproduced according to the present invention. Illustrated is a hollowcylindrical part 1 friction welded to an end cap 2, the end capincluding a flash trap in the form of a solid cylindrical portion 3 ofdiameter slightly less than the inner diameter of the cylindrical part1, extending along the cylindrical part 1 back from the region of theweld 4, and having an annular recess 5 in the region of the weld toreceive flash from the weld. Because the diameter of the solidcylindrical portion 3 is slightly less than the inner diameter of thecylindrical part 1, so that the concentricity limitation (accuracy underload) of the machine used does not result in "rubbing" or "pickup" awayfrom the friction surfaces, with consequent damage and creation of scaleand loose particulate matter, there is a clearance path 6 for smallparticulate matter to escape the trap, i.e. the annular recess 5. In theprior art, if friction welding was to be used in applications where suchcontamination was not permissible, the clearance path 6 had to be sealedin subsequent operations using epoxy, "O" rings, conventional welding,etc., rendering the production of the parts somewhat uneconomical.

In FIG. 2, the improvement offered by the present invention can be seen.The portion of the hollow cylindrical part 1 adjacent the non-recessedportion of the solid cylindrical portion 3 is rolled inwardly atdeformed area 7 so as to seal off the clearance path 6. Alternatively,as seen in FIG. 5, the flash trap may be deformed outwardly with thesame effect, as will be described in greater detail below.

The method produces this friction welded assembly with a tightly closedflash trap, on the friction welding machine as part of the machinecycle, while still allowing adequate clearance during the rotationalpart of the weld cycle.

The method is carried out by first running through the "weld" portion ofthe machine cycle in a conventional manner, complete with the usualclearance. Then, immediately at the completion of the weld portion ofthe machine cycle, while the material adjacent to the weld 4 is hot, thespindle of the friction welding machine is restarted, this time rotatingthe complete welded assembly, and a roller or rollers is/are broughtinto contact with the assembly opposite the "clearance" area and a forceis applied to the roller(s) so that material is upset or rolled into, orspun into, the flash trap clearance area, closing it tightly. The weldheat allows the upset to occur with much less force than if the assemblywere cold, and the subsequent shrinkage on full cooling ensures an eventighter seal. The roller force may be time and/or travel and/or forcecontrolled, prior to the machine spindle stopping and the assembly beingunloaded.

The deformed area 7 could be created by any suitable means, not beinglimited to rolling, and at any convenient time. For example, the partcould be reheated and then rolled, or cold rolling could be used (thoughpresumably with less satisfactory results).

It will be appreciated that the above description relates to thepreferred embodiment and method by way of example only. Many variationson the invention will be obvious to those knowledgeable in the field,and such obvious variations are within the scope of the invention asdescribed and claimed, whether or not expressly described.

For example, it should be apparent that the invention can be applied tovirtually any friction weld involving a flash trap where rolling or thelike could be used to seal the area of the flash trap, not beingrestricted to the specific parts described above. FIGS. 3 and 4 provideexamples of possible alternative flash trap configurations. In FIG. 3,the flash trap is formed by machining a reduced wall thickness section 8in the hollow cylindrical part 1. No recessed area is then required inthe solid cylindrical portion 3. In FIG. 4, the solid cylindricalportion 3 is considerably reduced in diameter, and the flash trap iscreated by virtue of the presence of a ring 9 inside the hollowcylindrical part 1. Whatever the configuration of the flash trap, theessence of the invention lies in creating the deformed area 7 aftercreating the weld, in order to seal the flash trap.

The alternative shown in FIG. 5 involves an annular conical flange 10 atthe inner end of the solid cylindrical portion 3. Instead of a roller orthe like deforming the wall of the hollow cylindrical part 1, a mandrelor punch 11 is used to deform the flange 10 outwardly, thereby effectingthe desired seal. The mandrel or punch 11 has a chamfered end to matchthe conical shape of the flange 10, so that axial pressure forces theflange radially. This alternative version of the product and method maybe desireable in many cases despite the added complexity of theoperation, as for example where the external cosmetics of the hollowcylindrical part 1 may be important, or where the wall thickness of thehollow cylindrical part 1 dictates against rolling it inwardly.

Such a part is formed by completing the weld and then forcing the flange10 against the mandrel 11 or vice versa. For example, after frictionwelding the parts in the conventional manner, the mandrel 11 could beautomatically advanced inside the hollow cylindrical part 1, andbackstopped. The hollow cylindrical part could then be unclamped, andthe welded assembly advanced toward the mandrel 11 by the weldercylinder, to deform the flange 10 and effect the seal.

What is claimed as the invention is:
 1. In a friction welded partcomprising firstly a hollow cylindrical part defining a cavity andsecondly a second part to which said hollow cylindrical part is frictionwelded, said friction welded part including a friction weld between saidhollow cylindrical part and said second part, and an internal flash trapin the region of the weld, said flash trap being defined between saidhollow cylindrical part and said second part, the improvement in whichone of said hollow cylindrical part and said second part is deformedtowards the other part at a location remote from the weld and betweenthe weld and the cavity without a weld formed at said location, so as toseal said flash trap from the cavity.
 2. A friction welded part asrecited in claim 1, in which said hollow cylindrical part is deformedinwardly in the region adjacent said flash trap so as to seal said flashtrap from the cavity at said location remote from the weld.
 3. Afriction welded part as recited in claim 2, in which said flash trap isdefined by a solid cylinder of diameter slightly less than the innerdiameter of said hollow cylindrical part, said solid cylinder projectingfrom said second part and extending along said hollow cylindrical partpast the region of the weld, said solid cylinder having an annularrecess in the region of the weld to receive flash from the weld, saidhollow cylindrical part being deformed inwardly against said solidcylinder at said location between said flash trap and the cavity.
 4. Afriction welded part as recited in claim 1, in which said flash trap isdefined by a solid cylinder of a diameter substantially less than theinner diameter of said hollow cylindrical part, said solid cylinderprojecting from said second part and extending along said hollowcylindrical part past the region of the weld, and having at itsprojecting end an axially and outwardly projecting conical flange, saidflange being deformed outwardly against said hollow cylindrical part atsaid location between said flash trap and the cavity.